1. Field of the Invention
The invention relates to laser machining a work surface using movable optics in situations where the laser beam spot width at the work surface must be precisely controlled.
2. Description of the Related Art
The use of lasers to machine a work surface, particularly cylindrical die cutting operations, is well known in the art.
U.S. Pat. No. 4,427,872, issued to Saunders on Jan. 24, 1984, discloses a rotary die cutting apparatus where the laser beam is fixed in position and the laser beam acts tangentially on a cylindrical work surface. This is representative of the type of apparatus that brings the work surface to the laser beam.
U.S. Pat. No. 4,742,206, issued Dietterich et al. on May 3, 1988, discloses another rotary die cutting apparatus where the laser is mounted on a carriage which is parallel to the axis of the rotating cylindrical work surface. Thus, the laser assembly is able to slide above the longitudinal axis, projecting the cutting laser beam on the cylinder transverse to the longitudinal axis of the cylinder.
Both devices permit the cylinder to be machined along its entire length which may exceed 100 inches. Typical die cutting cylinders are fabricated from wood and require precise slots, both in length and kerf, to be cut therein so that a plurality of tools, such as knifes or indentation rules, can be inserted. The kerf cannot vary more than 1 to 2 thousandths of inch. If it is too large, the tool will fall out under the pressure of use. If the kerf is too narrow, forcing the tool in the slot will cause the cylinder to deform and, perhaps, even crack under the strain.
While the above described devices are capable of making the desired cuts, both types of prior art rotating die cutting apparatus suffer from the necessity of moving the work piece to the fixed laser, or the laser along the work piece. Both prior art solutions require moving a large mass (either the rotating mechanism with the die blank to be cut or the high power laser that is to do the cutting) along a predetermined and accurately defined path. The machinery and control required to accomplish this adds considerably to the cost of the machine.
A rotary die cutting apparatus that uses a fixed laser and eliminates the necessity of moving the work piece relative to the laser, other than simply rotating the cylinder, is not found in the prior art.